A number of approaches can be used to whiten teeth. One common approach is to use abrasives (e.g., in toothpastes and prophylaxis pastes) in combination with a polishing action to treat discolorations and stains on the surface of the teeth. Abrasives, however, offer limited effectiveness in whitening the teeth; because abrasives work only on the surface of the teeth, they do not appreciably change their intrinsic color.
Another approach is the use of chemical whitening actives in a composition to intrinsically and extrinsically whiten teeth. A chemical whitening active is applied to the teeth for a period of time to allow the active ingredient to act upon the teeth to provide an improvement in the whiteness of the teeth. Whiteners are commonly applied to the teeth via toothpastes, rinses, gums, floss, tablets, strips and trays.
A common chemical whitening active is Hydrogen peroxide (H2O2). Such common devices as plastic strips and trays can be used to apply peroxide for certain contact times beyond those achievable with typical tooth brushing. Concentration of the whitening active, contact time, and number of applications are some of the primary parameters that dictate the rate and amount of whitening achieved with peroxide-based tooth-whitening compositions. Whitening products using a strip of material in combination with a chemical whitening active are described, e.g., in U.S. Pat. Nos. 5,891,453 and 5,879,691, the disclosures of which are incorporated herein by reference.
Efforts to increase the efficacy of whitening products have included increasing the concentration of peroxide for faster whitening per time of use. Maintaining the peroxide on the tooth surface for longer contact times and/or for an increased number or frequency of applications has also been employed for improved whitening. While increasing concentration, increasing wear time, and increasing number of applications can achieve higher degrees of tooth whitening from a tooth-whitening product, each of these parameters also may have a negative impact on the consumer's experience.
Increasing the concentration of the peroxide in the whitening composition, while holding all other parameters essentially constant, can result in increased tooth sensitivity and soft-tissue irritation. Sufficiently high concentrations of peroxide may require a physical barrier, such as a rubber dam, to prevent the peroxide from contacting and burning the soft tissue, thereby making the use of the high peroxide concentrations inconvenient and impractical for unsupervised and repeated use, such as, e.g., repetitive at-home applications. In fact, even conventional tooth whitening compositions used by dentists and having a peroxide concentration equivalent to approximately 13% hydrogen peroxide, often require utilization of a rubber dam to protect the patient's soft tissue during the bleaching process during the office treatment. Increasing the use time and/or frequency generally increases the amount of tooth sensitivity and gingival irritation—and thus makes the product less convenient to use.
The mechanism of bleaching by peroxide involves the reduction of yellowness by generating singlet oxygen through the breakdown of hydrogen peroxide to convert C═C bonds to carbon single bonds (C-x). C═C bonds disproportionately absorb blue light (450 nm-470 nm) and thus appear as yellow under full-spectrum light, whereas C-x bonds do not. The acceleration of this chemical reaction under the application of blue light is reported widely in the literature, with one hypothesis being that application of blue light elevates outer-shell electrons in C═C pairs to a higher quantum level, or energy state, increasing their ability to bond with available peroxide derivatives. The intensity of light needed to elevate electrons to a higher energy state is not known; however, the hypothesis supports the premise of a threshold intensity above which the reaction is accelerated and below which the reaction is not accelerated. To this end, it seems desirable to apply light above threshold intensity to as many teeth as possible, but it is of little benefit to deliver light substantially beyond the threshold intensity.
Use of blue light to accelerate teeth bleaching in the dental office has been in practice for more than ten years. Such companies as Zoom! and Britesmile provide high-power, high-intensity light-delivery systems to dental professionals for use with expert-applied, high-concentration peroxide chemistries such as carbamide peroxide and hydrogen peroxide. These systems are designed to provide light of sufficient intensity and of sufficient duration to accelerate whitening on all anterior surfaces of maxillary and mandibular teeth. However they have certain limitations, including lack of portability and comfort, requisite operator's skill, inflexible power requirements; and the process is time-consuming. More specifically, such systems are typically large, free-standing or floor-mounted appliances; that are designed to be operated exclusively by trained dental professionals (and cannot be self-administered); the application is typically uncomfortable to the patient and lasts for more than ten minutes—and in some cases multiple doses exceeding individually or in part ten minutes. In addition, such systems require the use of paint-on, high-concentration peroxide chemistries, along with including retractors and gingival barriers. Lastly, they are designed to be powered directly from 110 VAC power—as opposed to batteries.
A variety of blue-light devices exist in the market to deliver some form of light, typically blue light, to anterior surfaces of some teeth while said teeth are in the presence of peroxide chemistries. These devices fall into two categories: Rechargeable-cell-driven devices and primary-cell-driven devices. Rechargeable-cell-driven devices include at least one rechargeable battery, typically a Ni-Cad or Lithium chemistry battery, which by its nature and chemistry is capable of delivering a high current output relative to its capacity. Such cells are chosen for this attribute and are typically used also in applications requiring high current output, such as power tools, portable appliances, cellular telephones, etc. These cells provide an advantage in light-emitting tooth bleaching devices by supplying current at a very high intensity to an array of multiple light sources, such as LEDs, typically over a long duration, exceeding for example one minute, two minutes, five minutes, or ten minutes. The disadvantage of these devices is that they cannot be used for a full regimen of treatments, for example seven treatments, fourteen treatments, twenty treatments, or twenty-eight treatments, without being recharged at some point between treatments or doses. Recharging is an inconvenience to the user, adds complexity to the device, and necessitates typically an additional device or accessory to connect the device to mains power from the wall. Further, chemistries typically used in rechargeable battery cells do not maintain their charge and capacity during dormant periods as well as do the chemistries used in primary cell batteries.
Primary-cell-driven devices emitting light, including blue light, are typically limited in one of the three ways: (1) intensity of light delivered, (2) area coverage of teeth, or (3) physical weight of the device. Devices delivering high intensity light to a large area of teeth (including all maxillary and mandibular anterior teeth) typically have one or more heavy, large primary cells. Devices having a low total weight of primary cells, however, can typically deliver only low-intensity light to all intended teeth, or can deliver high intensity light only to a subset of all intended teeth. Further, many primary cells cannot deliver a full regimen of treatments including even two of three requirements (intensity, area coverage, and low weight) without the replacement of battery cells between treatments.
Therefore, it would be advantageous to provide a device that (1) delivers light of sufficient intensity and duration to effect photo-activated bleaching of teeth when peroxide-based chemistries are applied to teeth, (2) to cover substantially all of the anterior surfaces of the maxillary and mandibular anterior teeth and (3) to provide a full regimen of uses without replacement of any battery cell, and wherein (4) the device has a weight that allows a user to self-administer the device without the use of hands for almost the entire duration of a treatment period, e.g., about 90% or more of the dose time or the treatment period.